Bicycle rollers have been in use since the early 1900's. A bicycle roller is a dynamometer for bicycles that is powered by the bicycle rider. A portable bicycle roller is traditionally comprised of one or more rotatable cylinders positioned so that the rear wheel of the bicycle rides on at least one cylinder, and one of the axles of the bicycle is fixed for stability. In the typical application, the front wheel is removed and the front fork of the bicycle is fixed to prevent the rider from tipping over.
In the prior art, the amount of power, or wattage, that the bicyclist is required to exert to ride at a given speed on a bicycle roller was determined by the amount of rolling resistance resulting from tire distress as the tire rolls over each of the cylinders plus the wattage required to drive any external devices which exert resistance on one or more of the cylinders. Rolling resistance is predominantly a function of the cylinder diameter, tire pressure, and bicyclist weight. Relying on these factors alone provides a linear relationship of resistance versus speed. Simple devices that add a predictable amount of resistance such as the magnetic eddy-current device of U.S. Pat. No. 6,857,992 (incorporated herein by reference) can be added externally to the cylinders, but these are undesirable since they provide a linear speed-to-resistance relationship.
Prior art bicycle rollers have a linear relationship of speed versus resistance. This solution is unsatisfactory; when beginning to pedal the bike from rest on rollers, low resistance is desired to allow the wheels to accelerate quickly enough to enable sufficient steering dynamics to keep the bicycle stable on the rollers. However, to obtain a meaningful training session, a high amount of resistance is desired when pedaling at a rate suitable to achieve cardiovascular exercise benefit.
To achieve both objectives it is desired to have a progressive resistance relationship with speed. In other words, a non-linear relationship between speed and resistance where the slope of resistance versus speed increases with increasing speed. This relationship is preferred because it more effectively simulates the non-linear effect of combined rolling resistance and wind resistance experienced when riding a bicycle in traditional fashion.
Eddy current devices use magnetism to generate electrical current in conductive materials when a magnetic field is placed in relative close proximity to the conductive material and relative motion of the magnet to the conductive material is present. The motion creates small electrical currents in the conductive material. The current creates a non-contacting friction between the two, along with generating heat in the conductive material. This heat must be dissipated in some fashion. Prior art resistance trainers utilize a large surface area on the roller(s) to dissipate the heat that is generated during use. For portable devices, parts must be made smaller to facilitate transportation and storage. This leads to a heat management issue, Prior art used a cylinder that contacted the rider's tire on the exterior and had the eddy current friction mechanism on the interior. With a large surface area, along with a good thermal conductor, it was possible to share the two uses with a single-walled cylinder. Reducing the size of the cylinder, while still maintaining the load capacity of the cylinder, it was necessary to add some additional form of thermal management. An improved eddy current device is needed.